This invention relates to image scanners and, more particularly, to a hand-operated optical scanning system comprising, a digitizing tablet containing position-sensing circuitry for outputting a signal indicating the position of a sensing coil in an x-y coordinate system associated with a working surface of the digitizing tablet; buffer memory means for receiving pixelized data associated with optical scanning of a document attached to the working surface of the digitizing tablet; a hand scanner for manual movement over the working surface of the digitizing tablet to scan a document attached to the working surface of the digitizing tablet, the hand scanner comprising, a case having a longitudinal axis, guide means carried by the case for allowing movement of the case over the working surface of the digitizing tablet only in a direction substantially along the longitudinal axis, read bar means carried by the case centered on the longitudinal axis and perpendicular thereto for optically scanning a one-dimensional line of pixels and for outputting a signal reflecting an instantaneous scanned image, and sensing coil means carried by the case centered on the longitudinal axis at a pre-established distance from the read bar means for being positionally sensed by the position-sensing circuitry of the digitizing tablet; and, logic means connected to outputs from the digitizing tablet and the read bar means and to the buffer memory means for continuously determining instantaneous positions and orientation of the read bar means in the x-y coordinate system as the hand scanner is scanned over a document attached to the working surface of the digitizing tablet, for continuously inputting the signal from the read bar means, and for storing pixelized information about the document into locations of the buffer memory means associated with respective locations of the document in the x-y coordinate system.
Image scanners for use with computers have long been recognized as providing great additional capability to the computer. Early scanners were very expensive, large, and cumbersome but did allow a page of previously-typed text to be scanned and optically character recognized and, thereby, input to the computer without the necessity for retyping. Similarly, drawings, and the like, could be scanned and digitized automatically, thereby eliminating the necessity for a human operator to manually digitize the data with a digitizing tablet system.
The compact optical scanning capabilities developed for facsimile machines and the like quickly led to the introduction of cheaper and les cumbersome page scanners for use with computers. More recently, such technology has been miniaturized and greatly simplified into hand scanning devices such as that shown in FIG. 1 which can be purchased for as little as one hundred dollars or less. Such hand scanners are not without certain limitations, however. The scanner 10 comprises a hand-holdable plastic case 12 in which is disposed a read bar 14 connected to the scanner logic 16. The read bar 14 is disposed over a slot 18 in the bottom of the case 12 so that as the case 12 is slid over a document or the like to be optically scanned, the read bar 14 can "see" through the slot 18. There are also rollers 20 mounted on shafts 21 passing through slots 22 in the bottom of the case 12 which roll along the document as the case 12 is "scanned" by hand over the document. The roller-carrying shafts 21 are mounted on their outer ends to supports 24 and are connected on their inner ends to a common transducer 26 which also outputs a signal to the scanner logic 16 indicating the direction and rate of movement of the rollers 20 and, thereby, the case 12 and read bar 14. The width of the scan pass is pre-determined by the length or width of the read bar 14. The length of the area that can be scanned by the scanner 10 is determined and limited by the size of a date input buffer (not shown) associated therewith. The scanner logic 16 of the scanner 10 only knows two things about the scanning action. The first is the width of the read bar 14. The second is that the read bar 14 is perpendicular to the path of movement of the case 12. Thus, as a user scans the case 12 over a document, the scanner logic 16 only knows that the read bar 14 is moving either forward or backward along a path of motion to which the read bar 14 is perpendicular. Thus, the pixelized data has no other orientation except for relation to the direction of scanning. Obviously, in such a system, larger areas cannot be scanned additively by multiple passes of the scanner 10.
Ichinokawa in U.S. Pat. No. 4,581,761, discloses a hand-held scanner 28 to be employed in combination with a digitizing tablet 30. The scanner 28 as shown in FIG. 2, again has a case 12, including a read bar 14 disposed over a slot 18. There is also scanner logic 16' connected to the read bar 14, as well as to a pair of sensing coils 32. The basic premise of the Ichinokawa scanner 28 is that a document to be scanned is temporarily attached to the surface of the digitizing tablet 30 and then scanned with the scanner 28. Since the position and orientation of the scanner 28 and read bar 14 are known in this system, multiple passes of the scanner 28 can be employed to create a larger scan input. This is because there are two coils 32 and, therefore, the position of the scanner 28 and thereby the read bar 14, on the surface of the digitizing tablet 30 (and thereby the document) can be determined. Thus, the scanner 28 knows the orientation of the scanned material with respect to up/down and left/right, as well as its exact position, so that the pixelized version of the scanned document can be created through multiple passes into a page memory (not shown) associated therewith. The problem with the Ichinokawa approach of FIG. 2 is that standard digitizer tablet systems do not employ circuitry for independently sensing the positions of dual coils and, therefore, a complete system including the scanner 28 and the associated digitizing tablet 30 would have to be implemented in order to commercially manufacture a hand-scanning system according to the Ichinokawa approach.
Wherefore, it is the object of this invention to provide a hand-held scanner for use with a standard, single-coil-sensing digitizing tablet system which can scan a large document in multiple passes through the use of positional and orientation information provided by the digitizer table portion of the system.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.